New Bottom Bracket

[Kell]

Just been looking on the Brompton site for new bottom brackets.

What's the general consensus with replacing these?

Like for like? i.e.:

Or some sort of upgrade? And if I was to go the upgrade route, then what do people recommend? What are the dimensions for a replacement? the one in the picture (from the Brompton website) looks to be stamped with 122.5, but most websites state 119.

 

[Tim Hall]

As with all "upgrades", what is it that you're trying to improve upon? Where do you think the existing one lets you down?

Or the short answer: UN55, you know it makes sense.

 

[T4tomo]

Does it even need replacing, they seem to go on forever.

 

[Brommyboy]

The newer (post 2013) Bromptons with the 'spider' crank use a JIS square taper BB, whereas the earlier ones use the ISO taper. Make sure you have the correct type when changing. I find that they are good for around 10000 miles in general.

 

[Kell]

I don't know if it does or doesn't need it. But I've heard some horrible noises coming from the drivetrain and I'm just thinking of possible cures.

 

[12boy]

I have been able to use ISO and JIS cranks and BBs interchangeably without issues, per the great Sheldon Brown, RIP. You know a BB is bad when it doesn't turn freely and when you grasp the crank arms and can wiggle them from side to side. BB Bearings can also make noise but a loose BB can creak. In the olden days some mechanics would wrap the BB threads with teflon tape to alleviate the creak, but I find heavy grease also helps. I never grease the spindle where the crank attaches although some do. I do grease the pedal threads with anti-seize compound but I do that whenever possible with all bolts and nut or other steel/ aluminum contacts except the crank arms and spindle and with Bromptons, the seat post. I bought a 119 mm bottom bracket and it works fine. If you use a Shimano BBS with the left side plastic, you do not tighten that too much since they crack fairly easily and they really don't do much except support the BB and don't need to be flush with the BB shell on the bike to do that.